Now we turn next year to a developing story a new scare from one of the nation's top labs. About the handling a potentially deadly viruses and bacteria anthrax smallpox. And now the flu tonight to labs forced to close after the third close call uncovered in just one month. ABC's chief medical editor doctor Richard -- investigates why this keeps happening. Tonight the Center for Disease Control bioterrorism lab in -- that shut down. After yet another frightening mistake. This time a sample of the deadly H five N one bird flu mistakenly shipped out to another lab. Potentially putting other scientists at risk it happened in May yet the CDC director informed just two days ago. When -- Got the call and I just couldn't believe it I was stunned and frankly appalled. This latest failure discovered during an investigation into -- -- by scientists were potentially exposed to anthrax in -- CBC eleven Atlanta. The revelation coming just two days after we learned dried smallpox samples. Which -- you know national agreement are only stored at too high containment labs in the world in Atlanta and Siberia. Were discovered in a cardboard box and an unsecured government lab in Maryland today we learned those samples were alive and potentially -- This string of incidents occurring at the top labs in the nation. This is the laboratory that we expect to have the highest level of safety in the world and if it can happen there it can happen almost any other lab. Tonight we asked the head of the CDC what went wrong. Is your cavalier attitude in the laboratories -- two laboratories that basically. We're not following the rules in terms of of handling dangerous germs we clearly need to improve the culture of safety. And make sure that there and every single one of CDC's -- These incidents are a wake up call. And Richie were once acting head of the CDC so what's next guest I mean this and it is demanding answers -- he's asking an outside group to help investigate. The big question tonight is who he is really monitoring CDC's labs. All right think -- so much on this big story.

This transcript has been automatically generated and may not be 100% accurate.

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